This invention is directed to systems and devices for measuring and/or regulating temperature of an electronic device or system at a remote location.
There are many situations where power is supplied to a device or system that is at a physically remote location. An example of such a device or system is a station for a cellular telephone network. Such stations can be located in direct sunlight in the middle of the summer, or in the middle of a desert. The temperatures can become excessive, where continued operation of the device or system can damage the system.
High temperature extremes can also be created at such remote locations by excessive demand by the device or system. This can also be aggravated by the ambient temperature. For example, electrical transformers serving a neighborhood can experience their highest load during peak summer heat, when air conditions are being run.
As noted above, such devices and systems can typically be in remote locations, sometimes miles from the power source. They are also typically physically separated from the area for monitoring and controlling the system (collectively referred to as the "management site"). (The power source can be located in the same facility as the management site, or separate from it.) The temperature sensing device, of course, must be located together with the device or system that it is to protect.
The contact or switch that is used to interrupt power from the load (i.e., the system or device) is also typically located at the remote location. Having the switch or contact located upstream (i.e., closer to the power source or management site) from the remote location is often not feasible or is uneconomical.
FIG. 1 gives a representative example of a system for temperature sensing and control of the power to a load at a site that is remote from the power source. (The dashed line in FIG. 1 adjacent the power is intended to represent a significant distance between the power supply and the load.)
In FIG. 1, the power source is electrically connected to the load through contact 10. Contact 10 is actually one of the contacts of relay 14, described further below. The contact 10 is in the same area as the load, remote from the power supply. On the load side of the contact 10, a tee in the line leads to ground through a bi-metallic switch 12 and a full wave rectifier 13. (A resistor regulates the power to the full wave rectifier 13.) When power is supplied to the full wave rectifier 13, it powers relay 14 with D.C. current. Relay 14 controls the state of contact 10, as represented by dashed line 16. (As noted above, contact 10 is typically part of the relay 14 device.) When the relay 14 is powered, contact 10 is closed. When power to the relay 14 is interrupted, contact 10 is opened.
In the normal operating state, power is thus supplied to the load. The bi-metal switch 12 is in a closed state, power is thus supplied to relay 14 (via rectifier 13), and contact 10 is closed. Bi-metallic switch 12 has a temperature threshold, above which it opens. (The threshold temperature is a function of a number of variables, such as the metals used, their configuration, etc.) When the temperature threshold of bi-metallic switch 12 is exceeded, power to rectifier 13 and thus relay 14 is interrupted and contact 10 is opened, thus interrupting power to the load.
Some bi-metallic switches reset (close) when they cool beyond a certain temperature. However, even if bi-metallic switch 12 in FIG. 1 automatically resets after cooling, power is not immediately restored to relay 14, because open contact 10 is interposed between the power an d the tee.
Thus, after bi-metallic switch 12 cools and closes, contact 10 must be reset in order to restore po w er to the load. Once contact 10 is re-set, power is also restored to the rectifier 13 and relay 14, which serves to maintain contact 10 close d.
Thus, the configuration of FIG. 1 requires that the contact 10 be manually re-set in order to restore power to the load. This in itself is not undesirable, since the load can represent a system that must be re-started under certain conditions or protocols. However, since contact 10 is often at the remote site in FIG. 1, having to manually re-set the contact 10 can be unacceptable.